configure: check for libstdc++.{so,dylib,a}

It's probably a good thing to check for at least one instance of
libstdc++.{so,dylib,a} at configure time. At least one is needed
by the companion libraries and gcc.

Original patch by Bryan Hundven <bryanhundven@gmail.com>

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

 reporter_name="Gustavo Zacarias <gustavo@zacarias.com.ar>"

 reporter_url="http://sourceware.org/ml/crossgcc/2011-03/msg00028.html"

 reporter_comment=""